Jerry Sims, who leads ARS research in Urbana, is
investigating how and why some weed seeds escape decay by soil microorganisms.
In photo, he holds a culture of giant ragweed seeds embedded in agar, some
overgrown with microorganisms. Click the image for more information about
it.

Seed-Rotting Microbes Sought to Battle Weeds

These banks are reserves of thousands, even millions, of weed seeds that lie
dormant beneath the soil awaiting favorable conditions to germinate, according
to Joanne
Chee-Sanford, a microbiologist with the Agricultural Research Service (ARS) in Urbana, Ill.

Since 2002, Chee-Sanford has been piecing together the conditions under
which certain fungi and bacteria will cause decay in dormant weed seeds,
killing them or diminishing their fitness. Classical biological control would
call for unleashing the microbes onto a targeted weed to fight it, but
Chee-Sanford has a slightly different tactic in mind. Rather than apply
microbes as biological control agents, she envisions bolstering the activity of
microbes that already occur in the soils naturally, possibly using an amendment
of some kind.

The problem is, seedbank soils are home to many microbial species with
different ecological roles to fill, notes Chee-Sanford, with the ARS
Invasive
Weed Management Research Unit. Some only eat carbon and other nutrients
exuded in the soil by seeds, while others use means such as powerful enzymes to
breach the seed, steal its nutrients and cause decay. Sometimes, seed decay is
a multimicrobe effort.

In one study, for example, 99 percent of velvetleaf seeds underwent
microbial decay after three months, particularly when the seeds were the only
carbon available as food. The prime decay agentsBacteroidetes and
Proteobacteria, found in many soilsare known to degrade natural
seed polymers. But Chee-Sanford is still trying to ascertain whether they were
the initial cause of the seeds' decay, or mere contributors.

Her efforts are part of a broader program within the Urbana unit to furnish
midwestern farmers with new weed-management systems that integrate biological,
chemical, cultural and mechanical control methods.

Read
more about the research in the May 2006 issue of Agricultural
Research magazine.